Method for forming refractory metal-silicon-nitrogen capacitors and structures formed

ABSTRACT

A method forforming a refractory metal-silicon-nitrogen capacitor in a semiconductor structure and the structure formed are described. In the method, a pre-processed semiconductor substrate is first positioned in a sputtering chamber. Ar gas is then flown into the sputtering chamber to sputter deposit a first refractory metal-silicon-nitrogen layer on the substrate from a refractory metal silicide target, or from two targets of a refractory metal and a silicon. N 2  gas is then flown into the sputtering chamber until that the concentration of N 2  gas in the chamber is at least 35% to sputter deposit a second refractory metal-silicon-nitrogen layer on top of the first refractory metal-silicon-nitrogen layer. The N 2  gas flow is then stopped to sputter deposit a third refractory metal-silicon-nitrogen layer on top of the second refractory metal-silicon-nitrogen layer. The multi-layer stack of the refractory metal-silicon-nitrogen is then photolithographically formed into a capacitor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is cross-referenced to Ser. No. 09/760,245, filed Jan.12, 2001, which is directed to a semiconductor device incorporatingelements of refractory metal-silicon-nitrogen and method forfabrication.

FIELD OF THE INVENTION

The present invention generally relates to a method for fabricatingsemiconductor devices incorporating capacitor elements formed ofrefractory metal-silicon-nitrogen and devices formed and moreparticularly, relates to a method for fabricating semiconductor devicesthat incorporates capacitor elements formed by depositing multi-layersof refractory metal-silicon-nitrogen in the same process chamber byvarying processing conditions and devices formed by such fabrication.

BACKGROUND OF THE INVENTION

In semiconductor fabrication, capacitors are frequently formed in-situin a semiconductor structure. For instance, an in-situ formed capacitorcan be found in a dynamic random access memory device. The processrequired for forming the capacitor is complicated. It involves thedeposition of different layers of materials by different chemicalprocesses, and most likely, in different process chambers. For instance,layers deposited of a polysilicon material are frequently used as theelectrode, while layers deposited of an insulating material such assilicon oxide are frequently used as the capacitor dielectric. Theprocess therefore requires multiple number of depositions, from multiplenumber of different materials conducted in multiple number of processchambers for the forming and patterning of the capacitor.

In modern semiconductor devices, refractory metals have been frequentlyused in semiconductor processes to form vias or contacts. However,refractory metal-nitrogen alloys have not been used widely in theprocessing of semiconductor devices. For instance, only recently, U.S.Pat. No. 5,892,281 describes the use of tantalum-aluminum-nitrogenalloys in semiconductor devices as a diffusion barrier and an adhesionpromoter. The patent discloses the use of Ta—Al—N in a semiconductordevice to prevent inter-diffusion between surrounding layers, forinstance, between two conductor layers; between a semiconductor layerand a conductor layer; between an insulator layer and a conductor layer;between an insulator layer and a semiconductor layer; or between twosemiconductor layers. A second use of Ta—Al—N is to promote adhesionwith adjacent layers, for instance, between two conductor layers;between a conductor layer and an insulator layer; between asemiconductor layer and a conductor layer; or between two semiconductorlayers. However, U.S. Pat. No. 5,892,281 does not teach any other usesfor tantalum-aluminum-nitrogen alloys in conductor fabrication.

It is therefore an object of the present invention to provide a methodfor forming a capacitor in-situ in a semiconductor structure that doesnot have the drawbacks or the shortcomings of the conventional methods.

It is another object of the present invention to provide a method forforming a capacitor in-situ in a semiconductor structure that requiresonly the deposition of a single material.

It is a further object of the present invention to provide a method forforming a capacitor in-situ in a semiconductor structure that requiresonly the deposition of a single material of refractorymetal-silicon-nitrogen in multiple layers.

It is another further object of the present invention to provide amethod for forming a capacitor in a semiconductor structure thatrequires only the deposition of a single material of TaSiN in multiplelayers under different processing conditions.

It is still another object of the present invention to provide a methodfor forming a capacitor in a semiconductor structure by depositingmultiple layers of a refractory metal-silicon-nitrogen each having adifferent stoichiometry.

It is yet another object of the present invention to provide a methodfor forming a capacitor in-situ in a semiconductor structure bydepositing multiple layers of a refractory metal-silicon-nitrogen eachhaving a different sheet resistance value.

It is still another further object of the present invention to provide amethod for forming a capacitor in a semiconductor structure bydepositing multiple layers of refractory metal-silicon-nitrogen in thesame chamber by varying a flow rate of partial pressure of nitrogen intothe chamber.

It is yet another further object of the present invention to provide asemiconductor capacitor structure which has a lower electrode, a middledielectric layer and an upper electrode formed of the same refractorymetal-silicon-nitrogen material but with different stoichiometry.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method for forming arefractory metal-silicon-nitrogen capacitor in a semiconductor structureand the structure formed are disclosed.

In a preferred embodiment, a method for forming a refractorymetal-silicon-nitrogen capacitor in a semiconductor structure can becarried out by the operating steps of positioning a preprocessedsemiconductor substrate in a sputtering chamber; flowing Ar gas into thesputtering chamber; sputter depositing a first refractorymetal-silicon-nitrogen layer on the substrate from a refractory metalsilicide target, or from targets of a refractory metal and a silicon;flowing N₂ gas into the sputtering chamber such that concentration ofthe N₂ gas in the chamber is at least 35% by adjusting the flow rate orpartial pressure of N₂; sputter depositing a second refractorymetal-silicon-nitrogen layer on top of the first refractorymetal-silicon nitrogen layer; stopping the N₂ gas flow into thesputtering chamber; sputter depositing a third refractorymetal-silicon-nitrogen layer on top of the second refractorymetal-silicon-nitrogen layer; and photolithographically forming thefirst, second and third refractory metal-silicon-nitrogen layers into acapacitor.

The method for forming a refractory metal-silicon-nitrogen capacitor ina semiconductor structure may further include the step of in-situannealing the capacitor at a temperature of at least 80° C., or the stepof flowing Ar gas into the sputtering chamber at a flow rate betweenabout 10 sccm and about 200 sccm, or the step of flowing N₂ gas into thesputtering chamber at a flow rate between about 1 sccm and about 100sccm. The method may further include the step of sputter depositing thefirst and the third refractory metal-silicon-nitrogen layer to athickness between about 100 Å and about 5000 Å, or the step ofdepositing the second refractory metal-silicon-nitrogen layer to athickness between about 100 Å and about 5000 Å. The method may furtherinclude the step of sputter depositing the first and the thirdrefractory metal-silicon-nitrogen layer each having a sheet resistanceof not higher than 50 ohm/sq., or the step of sputter depositing thesecond refractory metal-silicon-nitrogen layer which has a dielectricconstant greater than 7.5. The method may further include the step ofsputter depositing the first, second and third refractorymetal-silicon-nitrogen layer formed of a refractory metal selected fromthe group consisting of Ta, Nb, V, W and Ti.

The present invention is further directed to a semiconductor capacitorstructure which includes a lower electrode formed of a first refractorymetal-silicon-nitrogen material that has a sheet resistance not higherthan 50 ohm/sq; a middle dielectric layer formed of a second refractorymetal-silicon-nitrogen material that has a dielectric constant greaterthan 7.5; and an upper electrode formed of the first refractorymetal-silicon-nitrogen material.

In the semiconductor structure of a capacitor, each of the lowerelectrode and upper electrode is formed to a thickness between about 100Å and about 5000 Å, the middle dielectric layer is formed to a thicknessbetween about 100 Å and about 5000 Å. The refractory metal in the first,second and third refractory metal-silicon-nitrogen material is selectedfrom the group consisting of Ta, Nb, V, W and Ti. The first refractorymetal-silicon-nitrogen material has a sheet resistance of not higherthan 50 ohm/sq., while the second refractory metal-silicon-nitrogenmaterial has a dielectric constant greater than 7.5.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionand the appended drawings in which:

FIG. 1 is an enlarged, cross-sectional view of a semiconductor structurethat includes the present invention capacitor formed of three layers ofa refractory metal-silicon-nitrogen material.

FIG. 2 is a graph illustrating data obtained in deposition system #1showing the dependence of the sheet resistance of the present inventionrefractory metal-silicon-nitrogen material on the nitrogen content byadjusting nitrogen gas.

FIG. 3 is a graph illustrating data obtained in deposition system #1showing the dependence of the film uniformity of the present inventionrefractory metal-silicon-nitrogen material on the nitrogen content byadjusting nitrogen flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention discloses a method for forming a refractorymetal-silicon-nitrogen capacitor in a semiconductor structure by thein-situ forming of multiple refractory metal-silicon-nitrogen layerseach having a different stoichiometry on a semiconductor substrate andthen, photolithographically forming the multiple layers into acapacitor.

In the method, a preprocessed semiconductor substrate is firstpositioned in a sputtering chamber, Ar gas is then flown into thesputtering chamber to sputter deposit a first refractorymetal-silicon-nitrogen layer on the substrate from either a singlerefractory metal silicide target or from two targets of a refractorymetal and silicon. N₂ gas is then flown into the sputtering chamberuntil the concentration of the N₂ gas in the chamber reaches at least35% by volume by adjusting the flow or partial pressure of N₂, a secondrefractory metal-silicon-nitrogen layer is then sputter deposited on topof the first refractory metal-silicon-nitrogen layer. The N₂ gas flow isthen stopped to deposit a third refractory metal-silicon-nitrogen layeron top of the second refractory metal-silicon-nitrogen layer. After thedeposition of all three refractory metal-silicon-nitrogen layers, thelayers are photolithographically formed into a capacitor.

The present invention novel method may be followed by an optionalannealing step, wherein the capacitor structure is in-situ annealed at atemperature of at least 80° C., and preferably at a temperature of atleast 100° C. In the preferred embodiment, the Ar gas flows into thesputtering chamber at a flow rate between about 10 sccm and about 200sccm. The N₂ gas flows into the sputtering chamber during the formationof the middle refractory metal-silicon-nitrogen layer of high sheetresistance at a flow rate between about 1 sccm and about 100 sccm.

The invention further discloses a semiconductor structure of a capacitorthat is constructed by a lower electrode, a middle dielectric layer andan upper electrode. The lower electrode and the upper electrode are bothformed of a first refractory metal-silicon-nitrogen material that has asheet resistance not higher than 50 ohm/sq., while the middle dielectriclayer is formed of a second refractory metal-silicon-nitrogen materialthat has a dielectric constant greater than 7.5. Each of the lower andupper electrodes and the middle dielectric layer is formed to athickness between about 100 Å and about 5000 Å. The refractory metal inthe first, the second and the third refractory metal-silicon-nitrogenmaterials may be selected from the group consisting of Ta, Nb, V, W andTi.

Referring initially to FIG. 1, wherein an enlarged, cross-sectional viewof the present invention CMOS structure 10 with a capacitor stack 20 andan insulating material layer 12 formed on top is shown. A lowerelectrode layer 14, a dielectric layer 16 and an upper electrode layer18 are deposited of refractory metal-silicon-nitrogen materials thathave different stoichiometry and patterned over the diffusion barrier22. The insulating material layer 12 is deposited over the entire waferand contact openings 24,26 and 28 are etched which are latter filledwith a conductive material for forming electrical contacts to thediffusion barrier 22, the fuse 30 and the resistor 32, respectively. Inthe particular structure 10, shown in FIG. 1, the diffusion barrier 22prevents reaction between the lower electrode 14 and the polysiliconcontact via 34. The fuse 30 can be blown by forcing a large currentthrough the line-fuse material-via structure causing excessive heatingand melting in the fuse material and thus, loss of electricalconductivity.

A refractory metal-silicon-nitrogen material such as TaSiN has widerange of electrical resistivities depending on the stoichiometry of theTaSiN film. For instance, under normal DC sputtering conditions, filmsranging from 0.2 ohm-cm to nearly 10⁶ ohm-cm can be obtained by varyingthe nitrogen to argon ratio, i.e. from 4 vol. % to 50 vol. % byadjusting flow rate or partial pressure of nitrogen. At higher nitrogenratios, the film becomes insulating. The rate of increase in electricalresistance with nitrogen flow is monotonic, but the increases are muchsteeper at the higher nitrogen flow ratios.

Table 1 shows data on the relationship between the sheet resistance ofTaSiN films and the nitrogen percentage in the argon sputtering plasma.The materials listed in Table 1 were deposited in deposition system #1by adjusting the flow of N₂ into the Ar sputtering plasma. Theforty-nine point resistance measurement indicates that filmnon-uniformity increases as sheet resistance increases with greateramounts of nitrogen in the sputtering plasma. For example, a significantuniformity degradation occurs when nitrogen content increases from 40 to44, which is accompanied by a sheet resistance increases of an order ofmagnitude.

TABLE 1 N₂ in Ar Sputtering Plasma Rs Uniformity (vol. %) (Ohm/sq) (49points, %) 4 25.78 4.4 7 28.6 4.7 10 35.6 4.9 13 43.3 4.9 16 52.91 4.720 71.52 4.5 24 100.73 4.3 28 151.47 4.4 32 255.5 5.8 36 528.3 9.2 401727 17.2 44 14663 29.8 48 657770 44.3

Tables 2 and 3 show electrical properties for two TaSiN compositionswhich are insulators and can be used as a dielectric for a capacitorapplication. The materials listed in Tables 2 and 3 were deposited indeposition system #2 by adjusting the partial pressure of N₂ into the Arsputtering plasma. The capacitance, dissipation factor and dielectricconstant are shown as a function of applied frequency. For both films,the dissipation factor increased with increasing frequency whereas thedielectric constant is slightly lower at higher frequencies primarilydue to the higher loss (dissipation factor). The error in themeasurements is within ±10%.

TABLE 2 75.5 nm Ta:Si:N  7.7:30.7:61.6 (50% N₂ in Ar) FrequencyCapacitance Dissipation Dielectric (hz) (pF) Factor Constant 10 k 249 pF0.020 9.5 40 k 242 pF 0.021 9.2 100 k  238 pF 0.029 9.1

TABLE 3 58.7 nm Ta:Si:N  9.8:30.2:59.9 (30% N₂ in Ar) FrequencyCapacitance Dissipation Dielectric (hz) (pF) Factor Constant 10 k 282 pF0.010 8.4 40 k 274 pF 0.034 8.1 100 k  267 pF 0.050 7.9

As shown in Tables 2 and 3, the first sample in Table 2 has acomposition of Ta:Si:N of 7.7:30.7:61.5 and was prepared with 50 vol. %nitrogen in Ar plasma. The second sample shown in Table 3 has acomposition of 9.8:30.2:59.9 and was prepared with 30% nitrogen in Arplasma. The dielectric constant for the materials is shown as a functionof frequency by using a C-V measurement technique. The dielectricconstant decreases slightly with frequency due to the increase in thedissipation factor. The dielectric constant of the present inventionTaSiN is between about 8.0 and about 9.5.

Referring now to FIG. 2, wherein a graph plotted of sheet resistance ofthe TaSiN films as a function of nitrogen in the sputtering plasma isshown. FIG. 3 shows a graph plotted of resistance uniformity also as afunction of nitrogen in the sputtering plasma. The uniformity degradeswith higher percentages of N₂ in the Ar sputtering plasma.

The present invention novel method uses a multi-layer structure ofTaSiN, each with a different composition to achieve a final materialresistance. By utilizing the novel method, the process window for thefabrication process can be greatly increased. For example, it ispossible to obtain sheet resistance values between 15 K-ohm/square toinsulate with a better uniformity control.

Another benefit made possible by the present invention novel method isthe possibility for depositing multi-layer films in-situ to fabricate acapacitor. For example, first deposit a low sheet resistance film to apredetermined thickness as the bottom electrode, then deposit from thesame target but with a higher nitrogen flow to form a dielectric film,and finally deposit the third low sheet resistance film as the topelectrode. The present invention novel method may optionally include anin-situ annealing step such that the sandwiched film is ready forcapacitor patterning. This allows a reduction in the fabrication costand therefore, made the present invention method not only suitable forsemiconductor front-end applications, such as integration with devices,but also suitable for implementing high-density capacitors at thepackaging level.

The present invention novel capacitor may be formed by a refractorymetal-silicon-nitrogen material such as TaSiN. The refractory metal mayalso be selected from the group of elements consisting of Nb, V, W andTi. In a typical refractory metal-silicon-nitrogen composition of TaSiN,the composition may contain between about 5 at. % and about 55 at. % Ta,between about 10 at. % and about 45 at. % Si, and between about 30 at. %and about 80 at. % N. The semiconductor structure wherein the capacitoris formed may also include a conductive element used to establishelectrical connection with the capacitor. The conductive element may beformed of doped polysilicon, metal silicide, polycide, refractory metal,aluminum, copper and alloys thereof.

The refractory metal-silicon-nitrogen films, such as TaSiN, have theadvantage of being either insulating or resistive depending on the ratioof refractory metal to the silicon to the nitrogen. The films arethermally stable to annealing at temperature up to 800° C.

The present invention novel method can further be used to fabricate amodulated RC stack structure by modulating the mixture of nitrogen toargon during a sputtering deposition process.

The present invention novel method for forming refractorymetal-silicon-nitrogen capacitors and the structures formed havetherefore been amply described in the above description and in theappended drawings of FIGS. 1-3.

While the present invention has been described in an illustrativemanner, it should be understood that the terminology used is intended tobe in a nature of words of description rather than of limitation.

Furthermore, while the present invention has been described in terms ofa preferred embodiment, it is to be appreciated that those skilled inthe art will readily apply these teachings to other possible variationsof the inventions.

The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows:

What is claimed is:
 1. A method for forming a refractorymetal-silicon-nitrogen capacitor in a semiconductor structure comprisingthe steps of: positioning a preprocessed semiconductor substrate in asputtering chamber; flowing Ar gas into said sputtering chamber; sputterdepositing a first refractory metal-silicon nitrogen layer on saidsubstrate; flowing N₂ gas into said sputtering chamber such thatconcentration of said N₂ gas in said chamber is at least 35% byadjusting the flow or partial pressure of N₂; sputter depositing asecond refractory metal-silicon-nitrogen layer on top of said firstrefractory metal-silicon nitrogen layer; stopping said N₂ gas flow intosaid sputter chamber; sputter depositing a third refractorymetal-silicon-nitrogen layer on top of said second refractorymetal-silicon-nitrogen layer; and photolithographically forming saidfirst, second and third refractory metal-silicon-nitrogen layers into acapacitor.
 2. A method for forming a refractory metal-silicon-nitrogencapacitor in a semiconductor structure according to claim 1 furthercomprising the step of in-situ annealing said capacitor at a temperatureof at least 80° C.
 3. A method for forming a refractorymetal-silicon-nitrogen capacitor in a semiconductor structure accordingto claim 1 further comprising the step of flowing said Ar gas into saidsputter chamber at a flow rate between about 10 sccm and about 200 sccm.4. A method for forming a refractory metal-silicon-nitrogen capacitor ina semiconductor structure according to claim 1 further comprising thestep of flowing said N₂ gas into said sputter chamber at a flow ratebetween about 1 sccm and about 100 sccm.
 5. A method for forming arefractory metal-silicon-nitrogen capacitor in a semiconductor structureaccording to claim 1 further comprising the step of sputter depositingsaid first and said third refractory metal-silicon-nitrogen layer to athickness of between about 100 Å and about 5000 Å.
 6. A method forforming a refractory metal-silicon-nitrogen capacitor in a semiconductorstructure according to claim 1 further comprising the step of sputterdepositing said second refractory metal-silicon-nitrogen layer to athickness of between about 100 Å and about 5000 Å.
 7. A method forforming a refractory metal-silicon-nitrogen capacitor in a semiconductorstructure according to claim 1 further comprising the step of sputterdepositing said first and said third refractory metal-silicon-nitrogenlayer each having a sheet resistance of not higher than 50 ohm/sq.
 8. Amethod for forming a refractory metal-silicon-nitrogen capacitor in asemiconductor structure according to claim 1 further comprising the stepof sputter depositing said second refractory metal-silicon-nitrogenlayer which has a dielectric constant greater than 7.5.
 9. A method forforming a refractory metal-silicon-nitrogen capacitor in a semiconductorstructure according to claim 1 further comprising the step of sputterdepositing said first, second and third refractorymetal-silicon-nitrogen layers formed of a refractory metal selected fromthe group consisting of Ta, Nb, V, W and Ti.
 10. A method for forming arefractory metal-silicon-nitrogen capacitor in a semiconductor structureaccording to claim 1 further comprising the step of sputter depositingsaid first, second and third refractory metal-silicon-nitrogen layersfrom a sputtering target of refractory metal silicide.
 11. A method forforming a refractory metal-silicon-nitrogen capacitor in a semiconductorstructure according to claim 1 further comprising the step of sputterdepositing said first, second and third refractorymetal-silicon-nitrogen layers from two sputtering targets of arefractory metal and a silicon.